1. Field of the Invention
The present application relates to a method and apparatus for controlling more than one stepper motor using a single set of micro-controller outputs.
2. Detailed Description of Prior Art
In modern mechanical applications where precision turning is required it is known to use a stepper motor. A stepper motor operates by turning a shaft of the stepper motor a precise angle each time a positive pulse is received at the motor's input and by turning the shaft an equal angle in the opposite direction each time a negative pulse is received. Each of these partial turns is a referred to as a “step.” Stepper motors can have a varied number of steps per full revolution depending on the precision desired.
A stepper motor is ideal for uses requiring a high degree of precision, while not requiring a high magnitude of torque. A typical use meeting these criteria would be a gauge such as a fuel gauge or a coolant gauge in a vehicle. In these and similar cases it is desirable that the readings are accurate, and that instructions from a controller are interpreted precisely and identically each time they are sent in order to provide accurate feedback to an operator.
One disadvantage of using a stepper motor instead of a standard motor is that the control scheme of a stepper motor is more complex than that of a standard motor and requires more control signals from a controller. Additionally, due to the pulsed nature of a stepper motor control signal, a pulse width modulator is typically required to achieve accurate stepper motor controls.
As a practical rule all systems have a physical limit on the number of stepper motors they can control with a single micro-controller. Typically this limit is defined by the number of output pins on the micro-controller design selected for the system. For example, if a micro-controller design has eight output pins it can typically control a maximum of two stepper motors using a closed loop control scheme. When multiple stepper motors are used in a given system it is often the case that the required number of stepper motor control inputs will exceed the possible micro-controller outputs. It is known in the art to introduce additional micro-controllers when a single micro-controller cannot provide enough output pins.
A typical stepper motor utilizes two micro-controller outputs if it is controlled with an open loop or four micro-controller outputs if it is controlled with a closed loop. In a closed loop control scheme, two of the four pins are utilized for pulse signals, and two of the four pins are used for the feedback control. Devices using enough stepper motors to require multiple micro-controllers are common in the art.
It is desirable to minimize the number of micro-controllers contained in a particular device, however current systems do not have a way to reduce the number of microcontrollers and, at the same time, adequately control the required stepper motors.